A common type of loudspeaker in use today is known as a moving-coil loudspeaker. This speaker includes a transducer which converts electrical signals into mechanical energy. This mechanical energy is applied to a radiating diaphragm, which converts the mechanical energy into acoustical energy.
Moving-coil loudspeakers include a cone-shaped radiating diaphragm that is interconnected to a rigid “basket,” via a flexible suspension system. The basket is typically cast or stamped metal, or a resilient plastic, and is cylindrical in shape. The basket is designed for rigidity to avoid deformation as the main structural element of the loudspeaker.
A typical suspension system consists of one or more compliant members, a spider and a surround. The purpose of these elements is to maintain axial stability of the moving transducer while providing a restoring force to the speaker. Most moving-coil speakers also include a dust cap covering a central hole in the diaphragm to prevent contaminants—such as metal shavings—to enter the inside of a speaker. Such shavings can short out, or cause the speaker to malfunction.
At present, most moving-coil type speakers are conical in depth and cylindrical in shape. When such speakers are aligned in an elongated-array system, inter-element spacing is dictated by the basket frame dimensions. In addition to that, they are only tangentially coupled which leaves segments of baffle area between adjacent speakers that are not contributing to sound creation. This dead area (i.e. a discontinuity in the array) functions only as a diffraction boundary which degrades the sonic performance of the system.
Another class of speakers, known as “flat-panel loudspeakers” generally consist of a lightweight membrane, herein referred to as “acoustic-radiating diaphragm”, and a drive system. In one class of these flat-panel loudspeakers, the acoustic radiating surface is actuated into motion by an electrodynamic transducer which is mechanically coupled to the radiating surface. Measures are taken in the design of these panel speakers to ensure that the panel attains oscillation resonances which add to the acoustical output. These devices are generically called “multi-resonance” or “bending-wave” loudspeakers. A major drawback of multi-resonance/bending-wave loudspeakers, however, is their inability to accurately generate an acoustical reproduction of the electrical-stimulus signal, used to drive these speakers. More particularly, the undesired panel resonances color the impulse responses of these multi-resonance/bending-wave loudspeakers.
Another class of flat-panel loudspeakers utilizes the radiating membrane as an integral part of the transducer structure. This includes electrostatic and magnetostatic devices. In the case of both, they lack pistonic motion over the entire surface acoustic-radiating diaphragm to accurately reproduce low frequencies at equal amplitude levels to match the capabilities of the device at midrange and high frequencies. Generally, practical electrostatic speakers operate over a limited bandwidth, and require the support of additional conventional speakers for low frequency supplementation.
The foregoing describes only a sample of some drawbacks of conventional loudspeakers in use today.